1. Field of the Invention
The present invention relates in general to a ceramic composition for dielectric materials used as dielectric ceramic pastes or green sheets for forming electronic circuit boards, hybrid integrated circuits, integrated circuit packages, and multilayer ceramic structures. More particularly, the invention is concerned with such a ceramic composition for dielectrics, which is suitably fired in a non-oxidizing atmosphere.
2. Discussion of the Prior Art
In the art of fabrication of various ceramic circuit boards, in particular, multiple-layered ceramic circuit boards, there is known a method in which conductor patterns are screen-printed on a ceramic green body of a dielectric material, by using a conductor paste which contains, as a major component thereof, a noble metal such as gold, silver, platinum or their alloys, which is stable in an oxidizing atmosphere. The ceramic green body and the printed conductor patterns or circuits of the noble metal paste are then co-fired in the oxidizing atmosphere. Thus, a ceramic circuit board is obtained. Another method is known, wherein the conductor pattern is formed of a conductor paste whose major component is a non-noble or base metal such as copper, nickel or tungsten. In this method, a non-oxidizing atmosphere is used for firing the ceramic green body and the conductor paste.
The former method of fabricating a ceramic circuit board is advantageous in that the co-firing of the ceramic green body and the printed conductor pattern can be effected in air. However, this method can be practiced only at a high cost due to the use of gold, silver and other noble metals that are considerably expensive. Thus, the method suffers from a drawback in terms of manufacturing economy. On the other hand, the latter method which uses base metals as a conductor is advantageous in the material cost. However, the method has some deleterious drawbacks in the quality of the end product. Described more specifically, the firing operation in this latter method is carried out in a non-oxidizing atmosphere, and therefore an organic binder used as a component of a dielectric ceramic composition is not sufficiently decomposed in the non-oxidizing atmosphere. That is, the organic binder may be left in the form of carbon, whereby the obtained ceramic circuit board tends to have blackened surfaces, pin holes and blisters, and are liable to suffer from insufficient sintering and deterioration of electrical properties.
As described above, the known dielectric ceramic compositions with base metal conductors have problems of low rate of burnout or removal of an organic binder, and low degree of sinterability. In view of these problems, it is consid red very difficult to commercially practice the above-indicated method wherein a ceramic circuit board is fabricated by co-firing the ceramic dielectric composition containing a glass component, and a base metal conductor, in a non-oxidizing atmosphere.
However, efforts have been made to overcome the above-indicated problems or drawbacks associated with the technologies of co-firing a dielectric ceramic composition with a conductor of non-noble or base metal. For example, various ceramic compositions for dielectrics have been proposed, which include: a ceramic composition containing crystallizable glass; a ceramic composition containing a relatively large amount of alumina, zirconia or other refractory filler which is mixed with a glass component; a ceramic composition containing an oxide of high valence metal such as PrO.sub.2 ; and a ceramic composition containing an organic binder which is thermally decomposable at a low temperature. However, these proposed compositions have not satisfactorily eliminated the drawbacks experienced in the prior art.